Fabricating thermoset plates exhibiting uniform thickness

ABSTRACT

A method of manufacturing a flexographic plate having a uniform thickness comprises providing a thermoset layer having at least one uneven side; providing a thermoplastic layer having a first and a second side; attaching the first side of the thermoplastic layer to the uneven side of the thermoset layer thereby forming a flexographic plate; and calendering the flexographic plate via a series of heated pairs of rollers thereby creating a flexographic plate with a uniform thickness.

FIELD OF THE INVENTION

The present invention relates to manufacturing of flexographic plates,and more specifically to a method of formation of flexographic plateswith uniform thickness.

BACKGROUND

Prior to setting forth the background of the invention, it may behelpful to set forth definitions of certain terms that will be usedhereinafter.

The term “thermoplastic material” or “thermoplastic” as used herein inthis application, relates to a plastic that melts to a liquid whenheated and freezes to a brittle, very glassy state when cooledsufficiently. Most thermoplastics are high-molecular-weight polymerswhose chains associate through weak Van der Waals forces (polyethylene);stronger dipole-dipole interactions and hydrogen bonding (nylon); oreven stacking of aromatic rings (polystyrene). Thermoplastic polymerscan be re-melted and remolded. Many thermoplastic materials are additionpolymers; e.g., vinyl chain-growth polymers such as polyethylene andpolypropylene.

The term “thermosetting plastic”, “thermoset” or “thermoset material” asused herein in this application, relates to polymer materials thatirreversibly cure form. The cure may be done through heat (generallyabove 200 degrees Celsius), through a chemical reaction (two-part epoxy,for example), or irradiation such as electron beam processing.

Uncontrolled reheating of the material results in reaching thedecomposition temperature before the melting point is obtained.Therefore, a thermoset material cannot be melted and re-shaped after itis cured. Thermoset materials are generally stronger than thermoplasticmaterials due to a three-dimensional network of bonds, and are alsobetter suited to high-temperature applications up to the decompositiontemperature of the material.

The term “flexographic printing” or “flexography” as used herein in thisapplication, relates to a printing method that involves creating apositive mirrored master of the required image as a three-dimensionalrelief in a rubber or polymer material. A measured amount of ink isdeposited upon the surface of the printing plate (or printing cylinder)using an engraved anilox roll whose texture holds a specific amount ofink. The print surface then rotates, contacting the print material whichtransfers the ink.

Flexographic printing is a technologically challenging task. Minutedifferences in plate thickness, consistency and even surface energy cancause large deviations in ink transfer uniformity. Such deviations mayresult in poor quality printing and non smooth printed areas. Thethickness tolerances that are commonplace in the flexographic printingranges from −13 to +13 microns (μm). This value was chosen since theseare the tolerances available for printing drums, gears and cogwheels.

Manufacturing printing plates to a thickness uniformity of ±13 μm is notan easy task. Conventional and Laser Ablation Mask System (LAMS) platesare made of a thermoplastic material which gives leverage to fabricationwith systems such as extrusion followed by precise calendering of thesheet that is to be cut into plates. Plates that are imaged by directengraving, however, have to be thermoset. The plate material has to bethermoset to overcome the problem of edge melting by the engraving laseras well as to give chemical and solvent resistance and mechanicalstrength. Plate materials that are used in the direct engraving industryinclude rubber, crosslinked photopolymer and silicone based rubbers.Rubber plates are made by calendering the sheet material with heatedrollers to induce vulcanization. Photopolymer material is exposed to UVto induce crosslinking, introducing chemical and solvent resistance.Since photopolymer plates are transparent to UV and near IR, theseplates are engraved exclusively by CO2 lasers. Some of the directengraving plates on the market are ground to give the thicknessuniformity prior to imaging.

Fabricating thermoset materials in sheet form to a tolerance of ±13 μmfrom liquid or paste poses even more challenges. Thermoset pastes arerarely extruded for fear of clogging the extruder. Special precautionsmust be taken to avoid sticking of the material to the calenderingrollers, if such a system is chosen. In fact, many manufacturers ofextrusion equipment avoid experimenting with thermoset materials becauseof the difficulties involved in cleaning out the extruders. Casting thematerials does not give tolerances of the above mentioned figures overstandard plate sizes.

SUMMARY OF THE INVENTION

Briefly, according to one aspect of the present invention, there isprovided a flexographic plate comprising: a thermoset layer with atleast one uneven side; and a thermoplastic layer attached to one unevenside of the thermoset layer to form a flexographic plate.

Embodiments of the present invention provide a path to achieving therequired tolerances for flexographic printing plates with thermosetmaterials. The invention utilizes the advantages of thermoplasticmaterials in formability in order to give form to thermoset materials.Basically, a sheet of thermoset material that has less thicknessuniformity than required is attached to a thermoplastic material, andthe bi-layer or multilayered (in case more than just the thermoset andthermoplastic layers form the plate) sheet is calendered to the requiredtolerance by means already in existence for thermoplastic materials. Thethermoset layer will then form the image side of the printing plate.

These and other objects, features, and advantages of the presentinvention will become apparent to those skilled in the art upon areading of the following detailed description when taken in conjunctionwith the drawings wherein there is shown and described an illustrativeembodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter regarded as the invention will become more clearlyunderstood in light of the ensuing description of embodiments herein,given by way of example and for purposes of illustrative discussion ofthe present invention only, with reference to the accompanying drawings(Figures, or simply “FIG.”), wherein:

FIG. 1 is a schematic process diagram illustrating a process ofmanufacturing a flexographic plate comprising thermoplastic layer and athermoset layer according to some embodiments of the invention;

FIG. 2 is a schematic process diagram illustrating a process ofmanufacturing a flexographic plate comprising thermoplastic layer, athermoset layer and a dimensional support layer according to someembodiments of the invention;

FIG. 3 is a schematic process diagram illustrating a process ofmanufacturing a flexographic plate comprising a thermoplastic layer, athermoset layer, and a cushion layer according to some embodiments ofthe invention;

FIG. 4 is a schematic sectional view illustrating a flexographic platecomprising a thermoplastic layer, a thermoset layer, and a cushion layeraccording to some embodiments of the invention;

FIG. 5 is a schematic sectional view illustrating a flexographic platecomprising a thermoplastic layer, a thermoset layer, and a cushion layerattached to a dimensional support layer according to some embodiments ofthe invention;

FIG. 6 is a schematic sectional view illustrating a flexographic platecomprising a thermoset layer, and dimensional support layer positionedbetween two thermoplastic layers; and

FIG. 7 is a high level flowchart showing a method of manufacturing aflexographic plate having a uniform thickness according to someembodiments of the invention.

The drawings together with the description make apparent to thoseskilled in the art how the invention may be embodied in practice.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of the disclosure.However, it will be understood by those skilled in the art that theteachings of the present disclosure may be practiced without thesespecific details. In other instances, well-known methods, procedures,components and circuits have not been described in detail so as not toobscure the teachings of the present disclosure.

Prior to setting forth the detailed description of the invention, it maybe helpful to set forth definitions of certain terms that will be usedhereinafter.

The term “calendering” as used herein in this application, relates tothe process of using a series of hard pressure rollers for smoothing outa sheet of material that is inserted between the rollers.

The term “uniform” or “smooth” as used herein in this application,relates to a surface of a sheet exhibiting thickness differencessubstantially smaller than approximately 13 μm. Similarly, the term“uneven” as used herein in this application, relates to a surface of asheet of material exhibiting thickness differences substantially largerthan approximately 13 μm.

According to some embodiments of the invention, there is provided aprocess of manufacturing plates of substantial high level of thicknessuniformity by combining at least one sheet of thermoset material, thesheet not having the desired thickness uniformity and thermoplasticmaterials. There are existing methods of handling thermoplasticmaterials to get highly uniform printing plates; however, these methodsare not suitable for most thermoset materials.

FIG. 1 is a schematic process diagram illustrating a process ofmanufacturing a flexographic plate comprising thermoplastic layer and athermoset layer according to some embodiment of the invention. Accordingto some embodiments, there is provided a sheet of thermoset layer 12having an uneven surface 17. Thermoset layer 12 is being attached to alayer of a thermoplastic material 11. The combined thermoset layer 12and thermoplastic layer 11 are then calendered along plate movement path18 by a series of heated roller pairs 13 and 15 for achievingflexographic plate 14 exhibiting thickness uniformity in a manner thatresembles calendering a pure thermoplastic sheet.

According to some embodiments, thermoset layer 12 may be cast on asmooth surface to resulting in one smooth side 16 of thermoset layer 12and then laminated onto thermoplastic layer 11 having a thickness of atleast the largest level of non uniformity of the uneven surface 17 ofthermoset layer 12.

According to some embodiments, flexographic plate 14 is calendered bythe first pair of rollers 13 and further on by the last pair of rollers15 to desired predefined thickness uniformity. Additional pairs ofrollers may be used along plate movement path 18. The temperatureapplied on flexographic plate 14 decreases along plate movement path 18between each position of the pairs of rollers. Specifically, the firstpair of rollers 13 uses a higher temperature than the last pair ofrollers 15 in order to promote the cross linking as the material passesthrough the calendering system.

According to some embodiments, plate uniformity of smooth side 16 ofthermoset layer 12 may be achieved without casting thermoset layer 12 ona smooth surface during production. The pressure applied by thecalendering rollers 13 and 15 on side 16 in addition with the hardeningof the thermoplastic layer 11 thus pressing side 17 from the oppositeside of layer 12 thereby resulting in a uniform flexographic plate 14.

The high temperature applied on rollers 13 causes the thermoplasticmaterial 11 to melt and to fill the uneven side 17 of layer 12. As theprinting plate 12 progresses towards direction 18, the temperature atthe printing plate 14 movement path 18 decreases. The temperaturereduction causes the printing plate 14 to harden and form an eventhickness plate 14.

FIG. 2 is a schematic process diagram illustrating a process ofmanufacturing a flexographic plate comprising thermoplastic layer, athermoset layer and a dimensional support layer according to someembodiment of the invention. For structural support purposes at leastone additional two-dimensional structural support layer 21 such asPolyethylene Terephthalate (PET) layer may be used in the process.

FIG. 3 is a schematic process diagram illustrating a process ofmanufacturing a flexographic plate comprising a thermoplastic layer, athermoset layer, and a cushion layer according to some embodiment of theinvention. Specifically, cushion layer 31 may be made from eitherthermoset or thermoplastic materials. Such a material may be added aslong as there is at least one thermoplastic layer 11 thick enough tofill the non-uniform surfaces of the other layers: 12 and 21 or 31.

FIG. 4 is a schematic sectional view illustrating a flexographic platecomprising a thermoplastic layer, a thermoset layer, and a cushion layeraccording to some embodiment of the invention. Two-dimensionalstructural support layer 21 can be attached to the cushion layer 31 ofplate 14 for preventing plate deformation while mounted on the imagingdrum during the imaging process.

FIG. 5 is a schematic sectional view illustrating a flexographic platecomprising a thermoplastic layer, a thermoset layer, and a cushion layerattached to a dimensional support layer according to some embodiment ofthe invention. According to some embodiments, the position of cushionlayer 31 and two-dimensional structural support layer 21 can be swapped.

FIG. 6 is a schematic sectional view illustrating a flexographic platecomprising a thermoset layer, and two-dimensional structural supportlayer 21 positioned between two thermoplastic layers 11 and 61 of plate14.

FIG. 7 is a high level flowchart showing a method of manufacturing aflexographic plate having a uniform thickness, the method comprising:providing a thermoset layer having at least one uneven side 710;providing a thermoplastic layer having a first and a second side 720;attaching the first side of the thermoplastic layer to the uneven sideof the thermoset layer thereby forming a flexographic plate 730;Optionally attaching a dimensional support layer to the thermoplasticlayer 740; and calendering the flexographic plate via a series of heatedpairs of rollers thereby creating a flexographic plate with a uniformthickness 750.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the scope of theinvention.

Thus, this invention includes a method of manufacturing a flexographicplate having a uniform thickness, the method comprising:

providing a thermoset layer having at least one uneven side;

providing a thermoplastic layer having a first and a second side;attaching the first side of the thermoplastic layer to the uneven sideof the thermoset layer thereby forming a flexographic plate; and

calendering the flexographic plate via a series of heated pairs ofrollers thereby creating a flexographic plate with a uniform thickness.

-   -   The thermoplastic layer can comprise a dimensional support        layer.    -   Calendering the flexographic plate can be preceded by attaching        a dimensional support layer to the second side of the        thermoplastic layer.    -   Attaching a two-dimensional structural support layer to the        second side of the thermoplastic layer can be followed by        providing a cushion layer and attaching the cushion layer to the        dimensional support layer.    -   Calendering the flexographic plate can be preceded by providing        a cushion layer and attaching the cushion layer to the second        side thermoplastic layer.    -   Providing a cushion layer and attaching the cushion layer to the        second side of the thermoplastic layer can be followed by        providing a dimensional support layer and attaching the        two-dimensional structural support layer to the cushion layer.    -   The cushion layer can be a thermoset material or a thermoplastic        material.    -   The series of heated pairs of rollers are generally located        along a flexographic plate movement path and the heat of the        heated pairs of rollers can decrease along the flexographic        plate movement path.    -   The thermoplastic layer can have a thickness of at least 13 μm.    -   Additional layers can be added prior to calendering the        flexographic plate.    -   This invention also provides a flexographic plate comprising: a        thermoset layer having at least one uneven side; and a        thermoplastic layer having a first side and a second side,    -   wherein the at least one uneven side of thermoset layer is        attached to the first thermoplastic layer; and wherein the        attached thermoplastic and thermoset layers are calendered        thereby forming a flexographic plate having a uniform thickness.

PARTS LIST

-   11—thermoplastic layer-   12—thermoset layer with uneven face-   13—first pair of calendering rollers-   14—printing plate with thermoset (printing side) layer at the bottom-   15—last pair of calendering rollers-   16—thermoset layer smooth side—used for engraving-   17—uneven side-   18—direction of plate movement path-   21—two-dimensional structural support layer-   31—cushion layer—made from thermoset or thermoplastic material-   61—second thermoplastic layer-   710—providing a thermoset layer having at least one uneven side-   720—providing a thermoplastic layer having a first and a second side-   730—attaching the first side of the thermoplastic layer to the    uneven side of the thermoset layer thereby forming a flexographic    plate-   740—optionally attaching a dimensional support layer to the    thermoplastic layer-   750—calendering the flexographic plate via a series of heated pairs    of rollers thereby creating a flexographic plate with a uniform    thickness

1. A method of manufacturing a flexographic plate having a uniformthickness, the method comprising: providing a thermoset layer having atleast one uneven side; providing a thermoplastic layer having a firstand a second side; attaching the first side of the thermoplastic layerto the uneven side of the thermoset layer thereby forming a flexographicplate blank; calendering the flexographic plate blank via a series ofheated pairs of rollers thereby creating a flexographic plate blank witha uniform thickness; and engraving the flexographic plate blank to forma flexographic plate.
 2. The method of claim 1, wherein thethermoplastic layer comprises a dimensional support layer.
 3. The methodof claim 1, wherein calendering the flexographic plate is preceded byattaching a dimensional support layer to the second side of thethermoplastic layer.
 4. The method of claim 3, wherein attaching thedimensional support layer to the second side of the thermoplastic layeris followed by providing a cushion layer and attaching the cushion layerto the dimensional support layer.
 5. The method of claim 1, whereincalendering the flexographic plate is preceded by providing a cushionlayer and attaching the cushion layer to the second side thermoplasticlayer.
 6. The method of claim 5, wherein providing a cushion layer andattaching the cushion layer to the second side of the thermoplasticlayer is followed by providing a dimensional support layer and attachingthe two-dimensional structural support layer to the cushion layer. 7.The method of claim 3, wherein the dimensional support layer is a PETlayer.
 8. The method of claim 4, wherein the cushion layer is athermoset material.
 9. The method of claim 4, wherein the cushion layeris a thermoplastic material.
 10. The method of claim 1, wherein theseries of heated pairs of rollers are located along a flexographic platemovement path.
 11. The method of claim 10, wherein the heat of saidpairs of rollers decreases along the flexographic plate movement path.12. The method of claim 1, wherein the thermoplastic layer has athickness of at least 13 microns.
 13. The method of claim 1 whereinadditional layers are added prior to calendering the flexographic plate.